The chemical control of ventilation in patients with chronic obstructive pulmonary disease receiving various concentrations of inspired oxygen will be studied. In particular, the relationship of blood ammonia, and cerebrospinal fluid ammonia and amino acid concentrations to depression of ventilation during oxygen therapy will be emphasized. Based studies of the respiratory control system will be carried out in experimental animals, in order to develop an accurate dynamic model of the system. The interaction of the central and peripheral chemoreceptors will be determined by basilar artery and carotid artery perfusions. Neural afferent input from the carotid bodies will be measured.